Examples of a resistance-change memory that stores data by using the resistance change of a memory element are a magnetic random access memory (MRAM), resistive random access memory (ReRAM), and a phase-change random access memory (PCRAM).
As one of these resistance-change memories, an MRAM using the spin transfer writing method has been disclosed (reference: Jpn. Pat. Appln. KOKAI Publication No. 2008-47220). In this reference as shown in, e.g., FIG. 21, the memory cell area is reduced by decreasing the bit line pitch by using two layers of bit lines. To implement the above mentioned memory cell, however, it is necessary to implement a very difficult step of forming a contact extending from the upper bit line to a transistor by self-alignment over the lower bit line. This raises the possibility that the contact extending from the upper bit line to the transistor and the lower bit line shortcircuit.
In implementing a contact formation step that decreases the possibility like that, it is difficult to apply a low-resistance wiring material such as copper (Cu) to the bit lines, so a high-resistance wiring material such as tungsten (W) is applied. This reduces the read margin of a resistance-change memory such as an MRAM.